This invention relates to a method of diagnosing vibration of a rotary machine whose rotary shaft is journaled in journal bearings, and more particularly to a method of the kind above described in which the rotation of the rotary shaft of the rotary machine is continuously monitored for the purpose of detection of unusual vibration of the rotary shaft so that, in the event of occurrence of unusual vibration, the defective parts which would cause the unusual vibration can be determined.
Monitoring of vibration of rotary shafts of steam turbines and an electric generator in a power plant, such as an oil-fired power plant or an atomic power plant, occupies a great proportion of plant maintenance. FIG. 1 shows rotary units in such a power plant. In FIG. 1, rotary shafts of a high-pressure turbine 1, an intermediate-pressure turbine 2, a low-pressure turbine 3 and an electric generator 4 in a power plant are connected together and journaled in bearings such as journal bearings 5 to 10 as shown. A shaft vibration meter 11 is mounted on each of these journal bearings 5 to 10 to detect vibration of each of the rotary shafts 12 as shown in FIG. 2. The shaft vibration output signals 101 from the individual shaft vibration meters 11 are applied to a central control panel in which the input signals are sequentially scanned in the order of from the bearing 5 to the bearing 10, and the detected values of shaft vibration are displayed on individual meters for the purpose of monitoring the state of vibration of the shafts 12 and are, at the same time, recorded on a recording sheet by a recorder such as a dot-print recorder. When the amplitude of vibration of the rotary shaft of any one of the turbines exceeds a first allowable limit, an alarm signal is generated, and when it exceeds a second allowable limit larger than the first allowable limit, the turbines are tripped to be protected against damage. When such unusual vibration is detected, the detected shaft vibration signal 101 from the specific vibration meter 11 is amplified by an amplifier 13, and an amplified shaft vibration signal 102 from the amplifier 13 is then converted into a digital shaft vibration signal 103 by an A-D converter 14. The digital shaft vibration signal 103 from the A-D converter 14 is then applied to a Fourier analyzer 15 to derive a frequency spectrum signal 104 from the Fourier analyzer 15. This frequency spectrum signal 104 is examined for detecting variations in various frequency components so as to find the source of unusual vibration. Such a method of vibration diagnosis is described in, for example, an article entitled "Early diagnosis of dynamic unbalances and misalignments in large turbogenerators" which appeared in the magazine "Energia Nucleare" Vol. 23/n.5/Maggio 1976, pp. 271-277.
However, such a prior art method has not been satisfactory for the following reasons, among others, for the accurate identification of the source of unusual vibration:
(1) Difficulty is encountered in the comparison with past data of the frequency components.
(2) Continuous recording and tracing of records is required to detect trend in variation in the frequency components which may occur at indefinite timing. However, a great deal of labor is required to detect such variations whose occurrences are unpredictable.
(3) The factor of frequency components only is not enough for the accurate identification of the source of unusual vibration in many cases.